1. Field of the Invention
The present invention provides a monitoring method, a process and a system for recovering and reutilizing waste photoresist.
2. Description of the Related Art
Photoresist is an important chemical in the semiconductor process. After being exposed to light of proper wavelength, the exposed part of the photoresist material would undergo chemical reaction to become hardened by cross-linking or result in a compound that readily reacts with developer. Subsequently through the development process, the exposed pattern is developed.
In the semiconductor process, photoresist is commonly deposited on the glass substrate by spin coating. In order to obtain a uniform coat, photoresist is typically dispensed in excess amount. Generally, approximately one tenth of the dispensed photoresist is deposited on the glass substrate, while the rest are spun onto the interior walls or discharged into the collection tank. In the process of coating, the machine would rinse the interior walls periodically with solvent to wash off the photoresist thereon, and the solvent and the photoresist are flushed into the collection tank. The photoresist in the collection tank could have been diluted by the large amount of cleaning solvent, or become concentrated as a result of air suction, given the different coating process used.
In recent years, the development efforts have been focused on positive and negative photoresist as well as photoresist thickness. Newly developed thick photoresist is costly, thus increasing the production cost. The disposal of waste photoresist generated in the process also poses a problem. If the waste photoresist can be recycled and reutilized, it would help lower cost and reduce possible contamination.
The TW Pat. No. 389,850 discloses “a device for recovering photoresist discharged from spin coater”, using a driver motor in the spin coater set at alternating speed to collect the mixture of excess photoresist and cleaning solvent at predetermined interval. This patented technology only provides a method for recovering waste photoresist solution, but does not disclose the reutilization of the recycled waste photoresist. JP Patent 2002-23388 discloses an organic solvent recovering device and pattern forming method using this device, which provides a method of separating solvent and photoresist under reduced pressure. This method may recycle both the photoresist and the solvent, but does not provide in detail the monitoring of the separation procedure and quality control of the recycled photoresist. Another JP Patent No.11-133619 discloses a method for recycling photoresist, which collects waste solution containing waste photoresist and EBR and measures its solid content; if the solid content is too high, solvent is added to adjust the concentration; conversely excess solvent is evaporated. Subsequently the photoresist is filtered to remove particulate matters and pollutants. This patent only provides a concept of photoresist recovery, but does not propose the specific control conditions for adjusting and recovering the photoresist.
The present invention discloses a specific method for monitoring the regeneration of photoresist, which can monitor the quality of the recycled photoresist, and in combination with the photoresist regeneration process, recover waste photoresist and reuse it in all kinds of processes. The present invention not only helps lower production cost, but also minimize the pollution problem presented by the disposal of large amount of waste fluid.